House extension drawings in Harrow

Corner sites, balconies and other limits

Corner plots get specific treatment. Side extensions there need a subordinate roof and must keep 1 m from the corner boundary at first floor, and wedge-shaped first-floor side extensions are unacceptable. If your house stands on a corner, that shapes the plan before anything else does.

The guide is also firm on balconies. Roof balconies on extensions near a flank boundary are normally unacceptable, and flat-roofed extensions are usually conditioned against use as a balcony, so a flat roof should be drawn as a roof, not as a terrace.

Harrow has 31 conservation areas and 295 listed entries, and Green Belt covers 22 per cent of the borough, so edge-of-borough houses face the proportionality test as well.

Permitted development, prior approval or planning permission

The national limit for a single-storey rear extension is 3 m (attached) / 4 m (detached) beyond the original rear wall, single storey, no higher than 4 m. Domestic gardens covered 34.7 per cent of Harrow's land in the national Generalised Land Use Database. Where a house qualifies, a Lawful Development Certificate in Harrow records it.

Prior approval allows 6 m (attached) / 8 m (detached), single storey, height max 4 m; not on article 2(3) land or an SSSI, but Harrow's record is strikingly one-sided: in the latest published year it granted 27 larger home extension prior approvals and refused 108. Refusal is the more common outcome, so a full householder application, as in our planning drawings in Harrow, is often the safer path for a deeper extension.

The council's householder fee is £548, paid to the council.

How Harrow has been deciding householder applications

Harrow decided 917 householder applications in its latest published year and granted 81.7 per cent. 93.7 per cent were decided within eight weeks or an agreed extension.

The figures cover householder work of every size. They guide our timetable, and they do not forecast any one decision.

What the drawings include and what they cost

A Harrow set shows existing and proposed floor plans, elevations and sections, with the location and block plans and, where the guide asks for it, the angle and set-in lines. Extension drawings start at £695 including VAT, fixed before you commit.

A second chartered technologist checks every sheet, and if the council asks for changes we redraw at no charge until approval. Technical detail for building control follows in our building regulations drawings in Harrow.

If the work touches a shared wall or digs close to a neighbour's foundations, the Party Wall Act applies: Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations. The design must also meet the energy rules in Approved Document L: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. Glazing is limited too: Windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension floor area plus the area of openings removed or covered.

Other extension types and nearby boroughs

To focus on one form, see rear extension drawings in Harrow, double-storey extension drawings in Harrow or loft conversion drawings in Harrow. The borough overview is architectural drawings in Harrow.

Neighbours apply different rules. Compare house extension drawings in Brent, in Hillingdon or in Barnet.